DE2458037A1 - Heat resistant nonwoven fabrics of aromatic polymer fibres - bonded with material of same compsn - Google Patents

Abstract

Non-woven fabrics from staple or continuous fibres, of polyacrylamide, polyarylimide, polyaryl ester and/or polyaryl anhydride type, resistant to 350 degrees C and for long periods at >=200-250 degrees C, bonded with matl. of the same compsn. as the fibre and with long-term resistance to temps. of >=200-250 degrees C. The fabrics are used as pre-pregs for resin impregnation in electrical insulators e.g., for transformer and electric motors. The fabrics can be made in required thickness of below 200(30-80) mu with uniform porosity, giving consistent resin impregnation.

Description

High temperature resistant nonwoven fabric and process for its manufacture.

The invention relates to a high temperature resistant nonwoven fabric made of bound synthetic staple and / or continuous fibers and a method to its manufacture.

The nonwoven is characterized by a particularly good long-term temperature resistance as they are for numerous requirements, e.g. in the electrical insulation sector is desirable.

It is known to use nonwovens in the electrical insulation sector, e.g. to be used as a carrier material for insulation resins.

For this purpose, nonwovens are usually used, which are made from loog polyester fibers exist. These are then used for further processing in the form of so-called prepregs used. This means that they are reactive with a Insulation resin, mostly based on epoxides and polyimides, are soaked and the resin through a heat treatment is converted into the so-called B-stage. In this condition the resin is not yet fully cured.

Complete curing only takes place after installation, e.g. in a Transformer or an electric motor.

But it can also be that the nonwoven fabric without prior impregnation is processed and only then to achieve the insulation properties with a the above resins is drizzled on. As long as the later 0 operation Nonwovens are such nonwovens in combination with insulating resins, it can be used as an insulating material with great reliability.

Make the increasing demands on the electrical insulation sector the search for suitable insulation materials of higher resistance, in particular higher permanent temperature resistance necessary. Increasingly, insulation materials are required that are resistant to permanent temperatures of up to 250 cc.

The resistance to short-term temperature effects should thereby are even higher, expediently up to a range of about 350 ° C. Within of the temperature range specified above are, for example, ultra-fine glass fabrics and papers Can be used on the basis of polyarylamides. However, such products are usually not evenly structured to the required extent and often too thick.

just the increased temperature resistance are also small thicknesses below 200 xU, preferably from about 30 to 80 / u -desired. For optimal insulation To guarantee even at high voltages, the insulation resin should be very even taken up by the nonwoven fabric serving as a carrier will. this is not the case with the materials known up to now. The invention therefore lies the underlying task is a high temperature resistant and thin bonded Develop fleece of very uniform porosity.

According to the invention, a high temperature resistant nonwoven fabric is made from Bound synthetic staple and / or continuous fibers proposed that thereby is characterized in that the staple and / or continuous fibers from one up to about 3500 C temperature resistant and at least 200 to 2500 C permanent Polyarylamide, polyarylimide, polyaryl ester and / or polyarylanhydride exist that with a binding agent which is also permanently temperature-resistant at at least 200 to 2500 C. are provided, the composition of which corresponds to that of the fibers. Fibers and In particular, binders determine their composition and their properties also in their temperature resistance and resistance to external factors Influences largely matched. Polyarylamides have proven to be particularly suitable proven to be obtained by condensation from isophthalic acid and m-phenylene-diamine and up to about 35 0 C to short-term temperature effects resistant are. The long-term temperature resistance is certainly in the range of around 200 up to 250 ° C. In particular, those polyarylamides whose molecular weight is within the range of about 20,000 to 70,000. The binder has im essentially the same composition. Fibers and binders adapt to each other thus in terms of their properties in an optimal way to each other and to the made requirements.

The nonwovens according to the invention are produced in such a way that that first a fleece in a manner known per se on the dry or wet route from the high-temperature-resistant fibers is deposited, which then with the solution or dispersion of the binder whose composition is matched to the fibers is moved. The binder is then produced by precipitation or by coagulation deposited and thermally cured, the nonwoven fabric thus formed being expedient is post-treated by calendering. The binder can after a further also as expedient method is printed on the loose fleece and then cured using heat and pressure. Pressure and temperature are to be adjusted during compaction so that the crystalline structure of fibers and binders are retained. Both parameters are possibly based on to determine simple preliminary tests.

During the separation of the binding agent by precipitation or coagulation the fleece impregnated with the binding agent is passed through a water bath or exposed to the action of such a solvent that the deposition or Causes coagulation of the binder.

Here, too, the optimal temperature or the optimal solvent can be found if necessary, depending on the type of fiber used, by means of suitable preliminary tests determine.

Very high strength nonwovens are obtained by impregnation or Soaking a fleece made of polyarylamide staple fibers with the solution from comparable Polyarylamides. To achieve the binding of the individual fibers it is necessary, to remove the solvent used as gently as possible. When evaporating the solvent could, for example, damage the polyarylamide fibers enter through the vaporizing solvent at elevated temperature, the Use of the nonwoven as an insulation material would be restricted. It has Therefore, it has been shown to be expedient to use the pre-bonded fleece in the described manner in introduce a precipitation bath, e.g. a water bath.

It has been shown that the otherwise very inert folyarylamide fibers are so well bound by the polyarylamide precipitating in the water as a binder, that strengths result that are several times that of what otherwise hitherto customary nonwovens of corresponding weight classes is known. This in The polyarylamide precipitating in the solvent and water system affects the Fibers down and causes the bond.

After removing the water and any remaining water The nonwoven fabric is smoothed between hot calender rolls with a large amount of solvent. The amorphous polyamide which has precipitated is converted into the crystalline one State instead. At the same time, the calendering process ensures optimum and even resin absorption created the necessary structure. It is possible instead Water for precipitation also other liquids that are miscible with the solvent used or solvents.

Example li A solution of 87.5 r dimethylformamide (DMF) is prepared, 2.5 g LiCl and lo g folyarylamide with a MW of approx.

50, ooo resistant up to approx. 350 ° C.

The LiCl used serves as a catalyst during the dissolution process; only a slight swelling of the polyarylamide would be achieved with DMF alone. A fleece made of 30 g / m2 polyarylamide fibers is impregnated with this solution. The titer of the fibers used is 1.7 dtx and the cut length 50 mm. The wet pick-up is 500%, so that after drying there is a final weight of 45 g / m2 when using a 10% solution yields. The so-soaked fleece is immediately after impregnation driven into a water bath. The polyarylamide precipitates out of the solution and hits settle down on the fibers. The DMF goes together with the to dissolve as a catalyst used LiCl in the water bath. When using a countercurrent process, so the solvent DMF and LiCl are completely washed out of the pre-bonded fleece will. This is very important for later use as an insulation material. As the process continues, the water is squeezed off and dried the remaining water is removed. This results in a relatively voluminous, very open-pored and stiff material, which in many cases are already used in this form can. When calendering at 2000C, the already mentioned conversion from amorphous takes place in the crystalline state and one then obtains the for use as Insulation material suitable nonwoven fabric of very uniform thickness and porosity. With a final weight of 45 g / m, the thickness is approx. So to 55 / u.

Example 2: The binding of the fiber fleece can be analogous to Example 1 can also be done by printing or spraying the polyarylamide solution. It must on the viscosity, which is favorable for processing, which is determined by the concentration of the dissolved Polyarylamides can be controlled, be respected.

The further processing corresponds to example 1.

Depending on whether it is sprayed or printed, nonwovens can be used different porosity can be obtained.

Example 3: Instead of water, trichlorethylene (Tri) or other solvents miscible with DMF are precipitated.

In all cases it is important that the DMF and LiCl from the fleece Will get removed. The structure of the nonwovens obtained can vary depending on the precipitation medium be slightly different.

If you use water-immiscible solvents, e.g. trichlorethylene, so the LiC1 is in the DMF - Tri - LiCl system in the DMF. One directs this Mixing with water, the tri can be released and fed back into the process will. The water is distilled off from the mixture of water - DMF-LiC1 and the im Remaining DMF + LiC1 in the circuit again to dissolve new polyarylamide used.

Precipitation can be achieved as long as the concentration of the DMF in the precipitation bath does not exceed 50 - 60%.

With the concentration of DMF in the precipitation bath, the properties of the finished fleece can be influenced in terms of structure and porosity.

Example 4: As in Example 1, a fleece is prepared from high-temperature resistant Fibers based on polyarylamide, polyimide, polyesterimide, etc. and impregnated, soaks or prints this with a solution of a high-temperature-resistant resin, e.g. a polyimide resin which, in a suitable solvent, is e.g. N-methylpyrrolidone, is resolved. After removing the Solvent can be used at higher temperatures in connection with a calender process the hardening of the resin and thus the fleece bond take place. This can also be used to create high-temperature-resistant nonwovens, suitable for temperatures from 1650 to approx. 3 C.

Claims (9)

Patent claims: 1. High temperature resistant nonwoven fabric made of bonded synthetic Staple and / or continuous fibers, characterized in that the staple andSoder Continuous fibers made of a temperature resistant up to about 350 C and at least 200 Polyarylamide, polyarylimide, polyaryl ester permanently resistant to temperatures of up to 2500 C and / or polyarylanhydride, which are also at least 200 to 25o ° C permanent temperature-resistant binders are provided, its composition corresponds to that of the fibers. 2. Nonwoven fabric according to claim 1, characterized in that it contains fibers and binders made from polyarylamides having a molecular weight of about 20,000 to 7c.ooo contains. 3. Nonwoven fabric according to claim 1 to 2, characterized in that fibers and binders have a substantially critical line structure. 4. Nonwoven fabric according to claim 1 to 3, characterized in that it is uniformly about 20 to 300 n thick. 5. Nonwoven fabric according to claim 1 to 4, characterized in that it in the case of long-term exposure to temperatures within the range of about 200 to 2500 C. has about 60% of its tear strength at room temperature. 6. A method for producing a nonwoven fabric according to claim 1 to 5, characterized in that a in a known manner on dry or wet Paths laid fleece made of the high-temperature-resistant Fibers with the solution or dispersion of one in terms of its composition the fibers corresponding binder is added and the binder by precipitation or deposited by coagulation and then thermally cured and the nonwoven fabric formed in this way is optionally aftertreated by calendering. 7, a method for producing a nonwoven fabric according to claim 1 to 5, characterized in that a in a known manner on dry or A fleece made of the high-temperature-resistant fibers with a suitable dispersion of the fibers corresponding in terms of its composition Binder is printed and the binder is then thermally cured and the nonwoven fabric is optionally post-treated by calendering. 8. A method for producing a nonwoven fabric according to claim 6, characterized characterized in that the solution has a composition which corresponds to that of the fibers and up to about 3500 C temperature-resistant polyarylamide as a binder Loose fleece made of polyarylamide fibers is applied and the binder is then shrunk let the pre-bonded fleece is precipitated in a water bath. 9. A method for producing a nonwoven fabric according to claim 6, characterized in that characterized in that the binder with the help of trichlorethylene as a precipitant is deposited. lo. A method for producing a nonwoven fabric according to claim 6, characterized in that the binder in a precipitation bath containing up to 60% dimethylformamide contains, is deposited.